High-pressure fuel pumps for common rail fuel injection systems typically comprise one or more hydraulic pump heads where fuel is pressurised in a pumping chamber of the pump head by the reciprocating movement of a plunger. Typically, low-pressure fuel is fed to the pump heads by a low-pressure lift pump in the fuel tank, or alternatively by a transfer pump built into the high-pressure fuel pump. Once pressurised, the high-pressure fuel is fed from the pumping chamber to the common rail.
An inlet metering valve is used to limit the fuel that is fed to the high-pressure pump to be compressed and delivered to the common rail. A conventional inlet metering valve is effectively a controllable orifice, which acts to throttle the flow of fuel to the inlet valve of the high-pressure pump in order to control the pressure on the inlet side of the valve, which is typically spring-biased into a closed position. Accordingly, the pressure at the inlet side of the valve determines when the valve opens and the quantity of fuel delivered to the pumping chamber. In this way, only the amount of fuel required by the engine is delivered to the rail, thereby saving both fuel and energy compared to the situation where fuel is fed by the lift or transfer pump at constant full delivery.
However, there are a number of disadvantages to conventional inlet metering valves. In particular, such valves are expensive and add to the overall cost of the common rail injection system, which is undesirable. Secondly, inlet metering valves are relatively large and space consuming components. Thirdly, such valves are vulnerable to wear and to bad fuels, which has a detrimental effect upon the common rail injection system in which they are installed. Furthermore, the use of a conventional inlet metering valve means that the metering/rail pressure control mechanism is relatively far from the pumping chamber of the high-pressure fuel pump, which leads to undesirable delays in rail pressure control.
It is an object of the present invention to provide an inlet valve arrangement for the pump head of a high-pressure fuel pump which substantially overcomes or mitigates at least some of the above-mentioned problems.
For more information relating to an inlet valve arrangement for a high pressure fluid pump, the reader is directed to German patent application number 10-2008-018018 in the name of Continental Automotive GmbH.